Light filter with varying polarization angles and processing algorithm

ABSTRACT

A method, system and polarization filter for analyzing polarization properties of light are described, the method comprising: receiving image data from a plurality of image sensor cells, the image sensor cells comprised in an image sensing system; separating from the received image data polarization information and scene image data of a scene being captured; and processing the polarization information to deduce information. Additionally, a polarization filter for analyzing polarization properties of light is described, the polarization filter comprising an array of polarization cells in various directions of polarization, the polarization filter comprising a core array of at least horizontal polarization filter cell, vertical polarization filter cell, no-polarization filter cell and circular polarization filter cell.

BACKGROUND OF THE INVENTION

As the use of machine imaging and image processing develops in variousfields such as, for example, security, gaming, medicine, military,science and plastic arts, there is a growing need for highlyadvantageous image processing and analysis tools.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is a schematic illustration of an image sensing system foranalyzing polarization properties of light according to some embodimentsof the present invention;

FIG. 2 is a top view schematic illustration of polarization filtersub-arrays over an array of image sensor cells according to someembodiments of the present invention;

FIG. 3 is a sectional layered schematic illustration of a polarizationfilter, a wavelength filter and an image sensor arranged according tosome embodiments of the present invention;

FIG. 4 is a schematic illustration of an exemplary sub-array ofpolarization cells according to some embodiments of the presentinvention; and

FIG. 5 is a schematic flowchart illustrating a method for analyzingpolarization properties of light according to some embodiments of thepresent invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

Embodiments of the present invention may provide a light polarizationfilter and system for analyzing polarization properties of the lightcaptured by an image sensor. The light polarization filter according toembodiments of the present invention may reveal polarization propertiesof light captured by an image sensor. The information about polarizationproperties of the captured light may be used, for example, for imageanalysis by a human and/or by a processor, for example, in a machinevision and/or inspection systems. The analysis of the polarizationproperties may be used, for example, for deducing information about theobjects being imaged and/or for detection of certain elements and/orproperties of elements in the image. Additionally, in some embodimentsof the present invention, the information about polarization propertiesof the captured light may be used, for example, for processing and/orimprovement of the captured image, for calibration of the image sensorand/or for adjustment of light sources which may be used for capturingthe image.

A system according to embodiments of the present invention may beembedded in various kinds of imagers, cameras, scanners and other imagesensors, and thus, for example, may enable capturing an enhanced imagewith additional layers of information, which may be deduced from thepolarization properties revealed by the polarization filter.

Reference is now made to FIG. 1, which is a schematic illustration of animage sensing system 10 for analyzing polarization properties of lightaccording to some embodiments of the present invention. System 10 mayinclude an optical element 100 for collecting light, a polarizationfilter 200, a wavelength filter 300, an image sensor 400 and an imageprocessing system 500. Image processing unit 500 may include a processor560 and a non-transitory storage media 580, wherein a non-transitorystorage media may include any storage media accept for a transitory,propagating signal. Image processing unit 500 may communicate with imagesensor 400 and optionally with other elements of system 10 such as, forexample, wavelength filter 300 and/or optical element 100, via a two waydata link 510. System 10 may receive light via optical element 100 andlet it flow in the direction of arrow A. Although in FIG. 1 polarizationfilter 200 is shown between optical element 100 and wavelength filter300, the invention is not limited in this respect and polarizationfilter 200 may be positioned in other locations in system 10. Forexample, in some embodiments filter 200 may be located betweenwavelength filter 300 and image sensor 400 or, for example, may beembedded in image sensor 400. In other embodiments filter 200 may belocated, for example, in front of optical element 100 so that light maypass through filter 200 before collection by optical element 100.

Polarization filter 200 may include an array of polarization cells invarious directions of polarization, as will be described in more detailwith reference to FIG. 2. The array of cells may include a plurality ofrepeated sub-arrays of polarization cells in various directions ofpolarization, for example, in a repeated pattern. A polarization cell ofpolarization filter 200 may correspond to a respective cell orpredetermined group of cells of image sensor 400, so that substantiallyall the light received onto a cell or predetermined group of cells ofimage sensor 400 has passed through the respective polarization cell ofpolarization filter 200.

Wavelength filter 300 may include an array of wavelength filtering cellsin various colors, as will be described in more detail with reference toFIG. 3. The array of cells may include a plurality of repeatedsub-arrays of wavelength filtering cells in various colors, for example,in a repeated pattern such as, for example, in a Bayer filter. Asub-array of wavelength filtering cells may correspond to a respectivepolarization cell of polarization filter 200 and to its respective cellor predetermined group of cells of image sensor 400 so thatsubstantially all the light received onto a cell or predetermined groupof cells of image sensor 400 has passed through both the respectivepolarization cell of polarization filter 200 and the respectivesub-array of wavelength filtering cells in various colors. In someembodiments of the present invention, a wavelength filtering cell ofwavelength filter 300 may correspond to a predetermined respective cellor sub-group of cells, within the predetermined group of cells in imagesensor 400 which correspond to a certain polarization cell.

Accordingly, a cell of image sensor 400 may receive light in a certaincolor and certain polarization. Additionally, light component withcertain polarization property that passed a corresponding polarizationcell, may be received onto the corresponding predetermined group ofimage sensor cells after passing the respective wavelength filteringcells, and thus each image sensor cell in the predetermined group mayreceive the polarized light component in a different color. A data baseof relations of each image sensor cell with the respective wavelengthfiltering cell and polarization cell may be stored in non-transitorystorage media 580. Since the image sensor cells can be related to theirrespective polarization and color cells, comparison between theintensities of light received in several cells, for example, of adjacentgroups which relate to different polarization cells, may enablededuction of information, for example, about objects being imaged,illumination conditions, calibration of image sensor 400, wavelengthfilter 300 and/or optical element 100 and so forth. The analysis of thepolarization and/or color information may be performed, for example, byimage processing unit 500.

As mentioned above, image processing unit 500 may deduce calibrationinformation from the polarization and/or color properties of lightreceived onto cells of image sensor 400. In some embodiments of thepresent invention, based on the deduced calibration information, imageprocessing unit 500 may change calibration of image sensor 400,wavelength filter 300 and/or optical element 100, for example by controlmessages via data link 510.

Reference is now made to FIG. 2, which is a top view schematicillustration of polarization filter sub-arrays 210, which may beincluded in polarization filter 200 described above, over an array 420of image sensor cells 410 that may be included in image sensor 400,according to some embodiments of the present invention. A sub-array 210may include several polarization cells 211, 212, 213 and 214 withdifferent polarization properties. Although FIG. 2 depicts fourpolarization cells in each sub-array 210, any other number ofpolarization cells may be included in a sub-array 210, as long as atleast two polarization cells with different polarization properties areincluded in the same sub-array 210. For example, polarization cell 211may be a reference cell which transmits substantially all light,polarized and not polarized. Polarization cell 212 may transmit onlylinearly polarized light in one direction, for example verticallypolarized light. Polarization cell 213 may transmit only linearlypolarized light in another direction, for example horizontally polarizedlight. Polarization cell 214 may transmit only circularly polarizedlight. In some embodiments of the present invention, the samearrangement of polarization cells may be included in each sub-array 210,for example so as to form a repeating pattern of polarization cells.However, in other embodiments, different sub-arrays 210 may includedifferent polarizing cells and/or different arrangements. According tosome embodiments of the present invention, as illustrated in FIG. 2,each polarization cell 211, 212, 213 and 214 may be aligned over acorresponding group of image sensor cells 410, for example four sensorcells 410 as illustrated in FIG. 2, so that each polarization cell fitsin size, shape and alignment to a respective group of four cells 410. Inother embodiments of the present invention, an optical element betweenpolarization filter 200 and image sensor 400 may direct the lightpassing through a polarization cell 211, 212, 213 or 214 to therespective group of image sensor cells 410 and thus, for example, anexact superposition of a polarization cell over the respective group ofcells 410 may not be required.

Reference is now made to FIG. 3, which is a sectional layered schematicillustration of polarization filter 200, wavelength filter 300 and imagesensor 400 arranged according to some embodiments of the presentinvention. In the sectional view of FIG. 3, an exemplary portion ofimage sensor 400 is shown including several image sensor cells 410. Arespective portion of wavelength filter 300 may include a correspondingnumber of wavelength filtering cells 310 of various colors. A respectiveportion of polarization filter 200 may include two adjacent polarizationcells with different polarization properties, such as vertical andhorizontal polarization cells 212 and 213 or any other possiblepolarization cells as described above. Wavelength filtering cells 310may be arranged in repeating sub-arrays of wavelength filtering cells310 of various colors. For example, each of polarization cells 211, 212,213 and 214 or another may be aligned with a respective sub-array ofwavelength filtering cells 310 of wavelength filter 300. Additionally,each wavelength filtering cell 310 may be aligned with an image sensorcell 410, so that, for example, a certain cell 410 may receive lightthat passed through a respective wavelength filtering cell 310 in acertain color and through a respective polarization cell 211, 212, 213or 214 or another with a certain polarization property. Additionally,light component with Additionally, light component with certainpolarization property that passed a corresponding polarization cell, maybe received onto several image sensor cells 410 after passing respectivewavelength filtering cells 310, and thus each of the several cells 410may receive the polarized light in a different color. For this purpose,wavelength filter 300 and polarization filter 200 are interchangeable,i.e. the light may pass through polarization filter 200 and then throughwavelength filter 300 or vice versa.

Reference is now made to FIG. 4, which is a schematic illustration of anexemplary sub-array 210 of polarization cells of polarization filter 200according to some embodiments of the present invention. Sub-array 210may include a core array 250 of polarization cells 211, 212, 213 and 214with no polarization, vertical polarization, horizontal polarization andcircular polarization, respectively, as described in detail above withreference to FIG. 2. Additionally, sub-array 210 may include layer 260of polarization cells 1 to 12 surrounding core array 250 and layer 270of polarization cells 13-32 surrounding layer 260. Similarly, sub-array210 may include additional surrounding layers of polarization cells. Atleast some of the polarization cells in surrounding layers 260, 270 andso forth may have various linear polarization directions. In someembodiments of the present invention, in each layer, the linearpolarization cells may have different linear polarization directions,wherein the polarization phase difference between adjacent linearpolarization cells in a layer may be determined by dividing 360 degreesby the number of linear polarization cells in the layer. For example, inlayer 260, which may include, for example, 12 cells, the polarizationphase difference between adjacent cells may be about 30 degrees. Inlayer 270, which includes 20 cells, the polarization phase differencebetween adjacent cells may be about 18 degrees. Additional layers whichmay include more cells may provide smaller phase differences betweenadjacent cells, thus, for example, enabling detection of finer detailsof polarization information and/or more accurate deduction ofinformation based on the revealed polarization information. In someembodiments of the present invention, surrounding layers 260, 270 and soforth may include additional reference cells with no polarization suchas cell 211, optionally with different transparency levels. In someembodiments of the present invention, surrounding layers 260, 270 and soforth may include additional circular polarization cells such as cell214, optionally with different directions of circular polarization (suchas clockwise or counterclockwise circular polarization).

Although FIGS. 2, 3 and 4 illustrate square-shaped polarization cells,wavelength filtering cells and image sensor cells, it will beappreciated that according to some embodiments of the present invention,other geometrical shapes of cells are possible, such as, for example,circular or hexagonal cells. Additionally, different patterns and shapesof cell arrays and/or sub-arrays than shown in the drawings arepossible.

Reference is now made to FIG. 5, which is a schematic flowchartillustrating a method for analyzing polarization properties of lightaccording to some embodiments of the present invention. As indicated inblock 610, the method may include receiving, for example at imageprocessing unit 500, image data from a plurality of image sensor cells410 of image sensor 400. As described in detail above, image sensor 400,wavelength filter 300 and polarization filter 200 are aligned so that,for example, light component with certain polarization property thatpassed a corresponding polarization cell, may be received onto severalimage sensor cells 410 after passing respective wavelength filteringcells 310, and thus each of the several cells 410 may receive thepolarized light in a different color. Accordingly, based on datarelating each image sensor cell 410 to the corresponding polarizationcell and wavelength filtering cell, comparisons of image data receivedfrom several image sensor cells 410 may enable deduction of color,intensity and polarization data.

As indicated in block 620, the method may include separating from thereceived image data polarization information and scene image data of ascene being captured. The polarization information and scene image datamay be deduced for example, by comparing image data received from agroup of several image sensor cells 410. The analysis of the image data,including comparisons of the image data and deduction of information,may be performed, for example, by processor 560 of image processing unit500. The separated polarization information may be related to a certainimage pixel, which may be defined by the group of image sensor cellsfrom which the polarization information is being deduced. For example,the group of image sensor cells may correspond to a sub-array 210 ofpolarization cells, for example, as described above with reference toFIG. 2. The separated polarization information may include the degreeand direction of linear polarization, the degree and direction ofcircular polarization, and the total intensity. The polarizationinformation may be represented by Stokes parameters of polarization,from which the intensity and polarization information may be deduced.

As indicated in block 630, the method may include processing thepolarization information, for example, with relation to the respectivescene image data, in order to deduce information about the scene beingimaged, the image optical quality and/or the image sensor.

As indicated in block 640, processing of the polarization information,for example, with relation to the respective scene image data, may beperformed in order to deduce information about the scene being imagedsuch as, for example, illumination direction and/or intensity, physicalproperties of objects being imaged and/or detection of certain kinds ofobjects and/or scenes. For example, since reflection of light fromcertain kinds of materials affects the polarization of light in a knownmanner, information about the materials from which objects and/orsurfaces are made of may be deduced based on the polarizationinformation. Moreover, particular light sources with particularpolarization properties and/or patterns may be used for illuminating theimaged scene, for detection of particular kinds objects/surfaces basedon the polarization information received from image sensor cells 410.

Additionally, based on the polarization information, sizes and/or shapesof objects and/or distances of objects from the image sensor may bededuced. Based on analysis of the size and/or shape of an object, theobject may be identified. Additionally, based on the polarizationinformation, information about the medium between the image sensor andthe imaged object/surface may be deduced, such as, for example,information about materials existing in the air/water/other mediumbetween the image sensor and the imaged object/surface. Such informationabout materials may be indicative, for example, of air/water pollution.Additionally, based on the polarization information, information aboutnatural light sources and/or artificial light sources in the imagedscene may be detected, such as location, direction, intensity, glare,etc., for example, by analyzing the degree and direction of linearpolarization. The ability to process the polarization information inorder to deduce information about the scene being imaged, which isprovided by embodiments of the present invention, may be used, forexample, in remote sensing systems, machine vision systems, automaticsorting machines, computerized face and/or other feature detection,medical imaging and many other applications.

As indicated in block 650, processing of the polarization information,for example, with relation to the respective scene image data, may beperformed in order to deduce information about the optical and/or visualquality of the captured scene image. For example, certain kinds of colordistortions on the scene image may be correlated with high degree oflinear polarization, such as color distortions caused by lightreflections from surfaces in the scene. Other kinds of color distortionson the scene image may be correlated with low degree of linearpolarization, such as color distortions caused by unpolarized lightradiated from a light source in the scene. By analyzing the polarizationinformation, regions with color distortions and the nature of colordistortions may be detected and, thus for example, correction of theimage may be enabled. Additionally, based on the polarizationinformation, regions of haze and/or glare may be detected, which mayresult, for example, from the quality of the medium between the imagesensor and the imaged objects\ surfaces. The haze and/or glareproperties of the image may be isolated from the image data byidentifying the regions of polarization properties which correlate withthe haze and/or glare, thus, for example, enabling correction of theimage by subtraction of the haze and/or glare data.

As indicated in block 660, processing of the polarization information,for example, with relation to the respective scene image data, may beperformed in order to deduce information about the image sensor. Forexample, based on the polarization data and, for example, a givendirection of illumination, information about position and/or motion ofthe image sensor may be deduced. Additionally, based on the polarizationinformation, the level of dark current noise of the image sensor cellsmay be detected. Additionally, image sensor cells which relate todifferent polarization properties may require different exposure times,for example, because of different intensities. Therefore, based on theimage data received from an image sensor cell, under or over-exposure ofimage sensor cells which relate to particular polarization propertiesmay be detected.

As indicated in block 670, the method may include processing and/orenhancing and/or modifing image based on the deduced information. Forexample, based on the information about the optical and/or visualquality of the captured scene image, and based on correlation betweenthe visual quality of the image and polarization properties, the imagemay be processed to remove defects such as, for example, colordistortions, haze and/or glare. Additionally, as described above,polarization filter 200 may include repeating sub-arrays of polarizationcells of various polarization properties. Therefore, polarization cellswith similar polarization properties may be located in constantdistances over the polarization filter 200. Accordingly, image sensor400 may include groups of image sensor cells which correspond topolarization cells with similar polarization properties, wherein thegroups of image sensor cells may be located in constant distances overthe array of image sensor cells. This quality of system 10 may be usedfor providing additional features. For example, two similar imagesreceived on two image sensor cells a certain shift of distance betweenthem may by combined for extraction of three-dimensional and/or depthinformation on the imaged scene, for example, by triangulationcalculations. Therefore, a three-dimensional image may be created.

As indicated in block 680, the method may include communicatingcalibration data and/or commands to elements of system 10, such as, forexample, image sensor 400, wavelength filter 300 and/or optical element100 for performing calibration based on the deduced data. For example,calibration data and/or commands for adjusting the level of dark currentnoise of the image sensor cells and/or required exposure times may bedetected as described above and communicated to image sensor 400, and/orto individual image sensor cells, to wavelength filter 300 and/or tooptical element 100.

As indicated in block 690, the method may include outputting the deduceddata and/or enhanced image and/or modified image after processing byimage processing unit 500. For example, deduced information about theillumination, medium and/or image sensor may be communicated to a userand/or another processor, which may decide based on the information tomodify illumination, medium and/or image sensor parameters. For example,deducted information about the imaged objects, surfaces and/or mediumsmay be communicated to a user, storage medium and/or another processorfor further processing or any other use, according to the particularapplication.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A system for analyzing polarization properties of light, the systemcomprising: an optical element for collecting light; a polarizationfilter having an array of polarization cells in various directions ofpolarization; a wavelength filter comprising a plurality of repeatedsub-arrays of wavelength filtering cells in various colors, eachsub-array wavelength filtering cells correspond to a respectivepolarization cell of said polarization filter; and an image sensorcomprising an array of image sensor cells, wherein at least one of saidsub-arrays of wavelength filtering cells corresponds to a respectivepolarization cell of said polarization filter and to a respective groupof cells of said image sensor, so that each image sensor cell in saidrespective group of cells is configured to receive light that passedthrough both a respective polarization cell and a respective wavelengthfiltering cell.
 2. A system according to claim 1, further comprising animage processing unit for deducing polarization information based onimage data received from said image sensor.
 3. A system according toclaim 2, wherein said image processing unit is further configured forcommunicating calibration data deduced from the polarization informationto at least one of said image sensor, said wavelength filter and saidoptical element.
 4. A system according to claim 1, wherein said array ofpolarization cells comprises at least a core array of horizontalpolarization filter cell, vertical polarization filter cell,no-polarization filter cell and circular polarization filter cell.
 5. Asystem according to claim 4, wherein said array of polarization cellsfurther comprises at least one layer of polarization cells of variouspolarization properties, said layer surrounding said core array.
 6. Asystem according to claim 5, wherein at least some cells in saidsurrounding layer of polarization cells have each linear polarizationproperty in different direction.
 7. A system according to claim 6,wherein said at least some cells have linear polarization properties ina constant phase difference between adjacent cells.
 8. A polarizationfilter having an array of polarization cells in various directions ofpolarization, the polarization filter comprising a core array of atleast horizontal polarization filter cell, vertical polarization filtercell, no-polarization filter cell and circular polarization filter cell.9. A polarization filter according to claim 8, wherein said array ofpolarization cells further comprises at least one layer of polarizationcells of various polarization properties, said layer surrounding saidcore array.
 10. A polarization filter according to claim 9, wherein atleast some cells in said surrounding layer of polarization cells haveeach linear polarization property in different direction.
 11. Apolarization filter according to claim 10, wherein said at least somecells have linear polarization properties in a constant phase differencebetween adjacent cells.
 12. A method for analyzing polarizationproperties of light, the method comprising: receiving image data from aplurality of image sensor cells, the image sensor cells comprised in animage sensing system of claim 1; separating from the received image datapolarization information and scene image data of a scene being captured;and processing the polarization information to deduce information.
 13. Amethod according to claim 12, wherein said separation of polarizationinformation and scene image data comprises comparison of image datareceived from several image sensor cells.
 14. A method according toclaim 12, wherein the deduced information comprises at least one ofinformation about the optical and/or visual quality of the capturedscene image, information about the scene being imaged and informationabout the image sensor cells.
 15. A method according to claim 14,further comprising processing the captured image based on the deducedinformation.
 16. A method according to claim 15, further comprisingoutputting at least one of the processed image and at least some of thededuced information.
 17. A method according to claim 16, furthercomprising communicating calibration data to elements of said imagesensing system.